Paint peeling composition and paint peeling method

ABSTRACT

A paint peeling composition contains as effective components thereof 17 to 25 weight percent of polyvinylalcohol or 2 to 12 weight percent of an acrylic resin or polyvinyl acetate and a subsstance which when heated is in the form of minute shells enclosing a gas or vapor, the shells being thermally expandable without rupturing.

REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 248,247, filedSept. 19, 1988, now U.S. Pat. No. 4,844,833, which, in turn, is acontinuation of application Ser. No. 007,300, filed Jan. 27, 1987, nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a paint peeling composition and a paintpeeling method for peeling off hardened or unhardened paint adhered toobjects not to be painted such as a duckboard, a floor, a table formounting thereon an object to be painted and a cover of an automaticcoater placed at a work place for painting.

Known methods for peeling off a thermosetting resin paint and the likeadhered to an object not to be painted are as follows:

(a) An object not to be painted is pre-coated with a paint peelingcomposition including as effective components thereof a thermoplasticresin paint and an organic solvent. Unnecessary paint adhered to thiscoating is peeled off by cracking the coated surface with a hammer andthe like (Japanese patent application published or laid open under SHOWA57-195774).

(b) The object not to be painted is pre-coated with a paint peelingcomposition including as effective components thereof coating-formingmaterial and a water-absorbent polymer. When unnecessary paint adheredto this coating is water-washed, the water-absorbent polymer reacts withthe water and then absorbs much of the same. A volumetric expansion of aratio of tens or hundreds times associated with this water absorptionserves to float the adhered unnecessary paint off the object not to bepainted and thereafter the floated paint is peeled off with a pallet,pliers, a hammer, a drill and the like (Japanese patent applicationpublished or laid open under SHOWA 57-19067).

(c) The adhered unnecessary paint is peeled off by being burnt in aburner and the like.

(d) The adhered unnecessary paint is peeled off by being re-solved by anorganic solvent.

(e) The unnecessary paint is peeled off by being submerged in boilingcaustic soda for approximately 12 hours to cause a chemical reactiontherein.

(f) The unnecessary paint is scraped off by a metallic pallet and thelike.

Problems with the above methods will be respectively discussedhereinafter.

(a) Much of the mechanical impact applied to the coated surface isabsorbed into the object per se through the coating. Therefore, aconsiderable impact is needed to cause the paint to crack.

(b) The contact between the water-absorbent polymer and the water neededfor the chemical reaction is interfered with by the coated surface. Or,if the paint peeling composition is pre-coated at a high temperature(about 300° C.), the water-absorbent polymer is carbonized to such anextent that it loses its water-absorbing expansion characteristics.Furthermore, this method is unfeasible for a water base paint includingwater such as a water solbule paint or a water-dilutable emulsion paint.

(c) This method is unfeasible for an unmovable object such as the floorof the work place and for an object subject to thermal transformation orto thermal solution. Moreover, this method tends to cause smokepollution or toxic gases such as nitrogen oxides.

(d) This method is unfeasible for an immovable object such as the floorof the work place and for a pre-painted object such as the cover of theautomatic coater.

(e) According to this method, the peeling operation is very timeconsuming. And, moreover, the object need undergo a neurtalizationprocess after the paint peeling operation; otherwise, the object mayincur rust. In addition, the caustic soda may pose human health hazard,and the waste liquid disposal of the caustic soda used for the peelingoperation is very costly.

(f) According to this method, if the adhered paint is a viscous,unhardened paint, the scraping operation is very labor-consuming.

SUMMARY OF THE INVENTION

Taking the above state of art into consideration, a first object of thepresent invention is to facilitate and speed up the peeling offoperation of the unnecessary paint adhered to the object not to bepainted and at the same time to provide a paint peeling compositionapplicable for a greater variety of objects. A second object of thepresent invention is to provide a paint peeling method by which thefirst object is achieved and at the same time a re-adherence of thepaint peeled off the object is prevented and the peeled paint is readilycollected.

The above first object of the present invention is achieved by a paintpeeling composition comprising as effective components thereof 17 to 25weight percent of polyvinylalchohol and a substance forming a group ofminute bubbles in the applied coating.

More particularly, this paint peeling composition is pre-applied to anobject not to be painted and then dried so as to form a coating on thesurface of this object. Then, as the painting operation proceeds, when apredetermined amount of unnecessary paint is adheredly accumulated onthe coating up to a point where peeling thereof is needed, if, forexample, this object is exposed to hot water, the adhered paint issoftened by the heat and at the same time monomer or solvent componentcontained in the paint generates bubbles thereby to lift up the paintand further the substance capable of forming minute bubbles in thecoating per se, e.g. synthetic resin balloons (microballoons) containedin the paint peeling composition e.g. expands volumetrically by the heatand the like and lifts the adhered paint off the surface of the objectnot to be painted. Moreover, polyvinylalcohol contained in the paintpeeling composition is re-solved or re-dispersed upon being exposed tothe hot water whereby the substance capable of forming small bubbles isfreed from the object thereby to free the paint. In this case, if thesubstance has such characteristics as to expand at a temperature higherthan that required for drying the paint, the disintegration of thecoating may be more effectively carried out since the coating issoftened by the heating. More specifically, a substance which expands ata temperature 20° to 50° C. higher than the drying temperature of thepaint is preferable for facilitating and speeding-up the coatingremoving operation.

After the peeling off operation, the object will be ready for the nextpainting operation after being water-washed, dried and then applied withthe paint peeling composition.

According to the above-described method, since strong mechanical impactis not applied to the unnecessary paint adhered to the object not to bepainted, the object does not suffer deformation or damage and theunnecessary paint may be peeled off effectively and speedily withoutfire hazard and human health hazard. Furthermore, since the paint may beremoved only by exposing the object to hot water and the like, nowater-washing or neutralization process of the waste liquid is necessaryand the method may be applied to objects unmovable from the work place,whereby the method is feasible for a greater variety of objects comparedwith the conventional methods.

The aforementioned second object of the present invention may beachieved by a paint peeling method in which the paint peelingcomposition comprising as effective components thereof 17 to 25 weightpercent of polyvinylalcohol and the substance capable of forming a groupof small bubbles in the applied coating is applied to the object not tobe painted and then dried to form the coating thereon. When apredetermined amount of unnecessary paint is adheredly accumulated onthis coating, this accumulated paint is peeled off by being exposed to aliquid prepared by water-diluting and then by heating a paintre-adherence preventing composition (acting also as a paint peelingpromoting composition) containing as an effective component thereofpolyvinylalcohol.

More particularly, the paint peeling composition is pre-applied to theobject not to be painted and then dried thereby to form the coating onthe surface of the object. When the unnecessary paint is adheredlyaccumulated on the coating, as painting operation proceeds, up to apoint where a peeling-off operation of the accumulated paint isnecessary, for example, the object is submerged in the heated liquidprepared by diluting by a predetermined amount of water and then byheating the paint re-adherence preventing composition containing as aneffective component thereof polyvinylalcohol. Then a protective colloidfilm which is non-viscous or only slightly viscous is formed on thesurface of paint adhered to the object and at the same time monomers orsolvents contained in the paint generate bubbles in response to the heatthereby to lift up the paint and further the substance capable offorming small bubbles, such as synthetic resin balloons, contained inthe paint peeling composition volumetrically expands in response to theheat and the like thereby to lift up the adhered paint off the object.In addition, as the polyvinylalcohol contained in the paint peelingcomposition is resolved or re-dispersed upon being exposed to theliquid, the volumetrically expanded substance such as the syntheticresin balloons is freed from the object to cause the paint to lift up byits own buoyancy to an upper portion of the liquid. In the aboveprocess, the resolved polyvinylalcohol is dispersed in the liquid toform the protective colloid film on the surface of the paint thereby toprevent the peeled paint from being re-adhered to other objects.Accordingly, the unnecessary paint is completely peeled off the object.

After the paint peeling operation, the object is taken out of theliquid, water-washed, dried and then is re-coated with the paint peelingcomposition. Then, the object is ready for the next painting operation.

On the other hand, because of the effect of the protective colloid film,the waste paint left in the liquid may be easily scooped out of theliquid even by a simply constructed mesh and the like. Further, sincethere is no paint left in the liquid, the remaining liquid is re-usablemerely by adding thereto some water for compensating the waterevaporated in the course of heating. As for the application of thismethod to an object immovable from the work place such as the floor, thepaint peeling composition is pre-applied to the surface of the floor andthen dried to form the coating thereon. Thereafter, when the paintpeeling operation becomes necessary as the painting operation proceeds,the aforementioned heated liquid is spilled over the floor. Then, thepaint is peeled off the floor without being re-adhered to other objectsin the same manner as in the above case.

Therefore, according to the present method, the unnecessary paintadhered to the object may be speedily, readily and safely peeled offwithout causing deformation or other damage to the object and withoutcausing fire hazard or human health hazard, and at the same time thepresent method is applicable to a greater variety of objects. Inaddition, since the paint peeled off the object becomes non-viscousbecause of the effect of the protective colloid film, the re-adherenceof the peeled-off paint is prevented and at the same time the collectingof the same may be effectively and easily carried out.

According to another aspect of the invention, 2 to 12 weight percent ofan acrylic resin or polyvinylacetate may be substituted for theaforementioned 17 to 25 weight percent of polyvinylalcohol. The acrylicresin or polyvinylacetate is used in the form of an aqueous emulsion andthe aforementioned percentage is based on the solid resin content of theemulsion. The term "acrylic resin", as used herein and as conventionallyused, includes polymethylmethacrylate, polyethylmethacrylate,polymethylethacrylate and polyethylethacrylate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the paint peeling composition and paint peelingmethod related to the present invention will be particularly describedhereinafter.

The paint peeling composition according to the present inventioncontains as its effective components 17 to 25 weight percent ofpolyvinylalcohol or 2 to 12 weight percent acrylic resin orpolyvinylacetate and a substance capable of forming a group of smallbubbles in a surface of coating per se to be formed on a surface of anobject not to be painted.

It is to be noted that the amount of polyvinylalcohol to be contained inthe composition as the effective component need be at least 17 weightpercent. That is, if the amount is less than this, the coating to beformed will have too small strength such that the coating may be easilycracked or peeled upon contact, for example, with safety boots worn byworkers. In addition, since the amount of water contained in the paintpeeling composition increases relatively, it takes longer to dry thecoating whereby the working efficiency deteriorates.

On the other hand, if the amount of polyvinylalcohol exceeds 25 weightpercent, increased viscosity of the paint peeling composition makes ittroublesome to apply the composition to the surface of the object. Thus,this is also to be avoided.

The substance for forming the bubbles may comprise a foamed hollowmatter such as shirasu balloons, glass balloons, carbon balloons andfoamed synthetic resin balloons or an unfoamed latently hollow mattersuch as unfoamed synthetic resin balloons. These materials may be usedsingly or in a combination. If the combination of these are suitablyarranged, it is possible to freely control starting temperature offoaming and a foaming multiplying ratio. Also, it is possible to use alow boiling solvent which is foamed by baking after the application ofthe coating to the object. Further, a chemical substance, such asazobisisobutyronitrile, may be used which chemically reacts withoutbaking to generate gas after the application of the coating, or ahigh-pressured Freon (i.e., fluorocarbon) gas may be used which isfoamed when air pressure is reduced to the normal level after theapplication of the coating.

In addition to the aforementioned effective components, a water-solublefilm forming binder such as butylcellulose or methylcellulose or varioustypes of additives such as thixotropy promoting agent, water-retentiveagent, antiseptic agent, rust inhibitor and defoaming or surface activeagent may be added to the composition.

In many painting factories, alkaline degreasing operation and zincphosphate operation in addition to water-soluble painting andelectrodeposition coating are carried out before the painting operation.In this case, if such a substance is selected for forming the coatingthat has alkali resistance or acid resistance property, it is possibleto continuously carry out all of the processing before painting, thepainting and baking-drying. Moreover, if there is provided a device forheating walls of painting booth such as a panel heater, the unnecessarypaint may be peeled off the walls merely by turning on the switch of theheater and then, for example, by tapping the walls with a hammer andsuch a great trouble as scraping with a pallet and the like is notneeded.

The paint peeling method related to the present invention will beparticularly described next. In this method, in addition to theabove-descrived paint peeling composition, a paint readherencepreventing composition acting also as a paint peeling promotingcomposition is used.

Of the above compositions, polyvinylalcohol contained in the paintpeeling composition has good re-solving characteristics and at the sametime has no blocking characteristics. Therefore, this polyvinylalcoholhas superior protective colloid characteristics for the paint and at thesame time has an effect to strengthen the film after drying.

A specific preparation of the paint peeling composition will bedescribed next.

    ______________________________________                                        polyvinylalcohol   21 weight percent                                          (average polymerization                                                       degree 500,                                                                   saponification degree                                                         88 mol %)                                                                     synthetic resin micro balloons                                                                    8 weight percent                                          methylcellulose     2 weight percent                                          water              68 weight percent                                          ______________________________________                                    

In addition to these, thixotropy promoting agent, water-retentive agent,antispectic agent, rust inhibitor, defoaming or surface active agent andthe like are conveniently added thereto.

An actual preparation of the above composition is carried out asfollows.

Firstly, a solution tank is filled with water of 15° to 25° C. andpolyvinylalcohol is added thereto under stirring. Then, this liquid isheated under sufficient stirring up to approximately 90° C. In about 30minutes, the polyvinylalcohol is completely dissolved. To this solution,methylcellulose is added. After cooling of this mixture to below 30° C.,synthetic resin microballon and the other additives are added theretoand the mixture is stirred and dispersed at a high speed. In thisembodiment, it is to be noted, the employed synthetic micro balloons forreinforcing the coating after drying starts foaming at approximately 60°to 80° C. and foams most actively at 100° C.

The obtained paint peeling composition was applied to a piece ofduckboard (20 cm square) by way of example of the object not to bepainted. Since the composition contains a relatively small amount ofwater, the drying speed was considerably shortened and at the same timesince the formed coating had sufficient strength because of its largethickness, the coating was not peeled off the board when this wasstamped upon by safety boots of a worker and the like.

For metalic objects, it is to be noted, various kinds of starches werefound effective as an additive for securing the coating on the surfaceof the object.

A specific preparation of the paint readherence prevention compositionwill be described next.

    ______________________________________                                        polyvinylalcohol 10 weight percent                                            (average polymerization                                                       degree 1700,                                                                  saponification degree                                                         88 mol %)                                                                     water            85 weight percent                                            ______________________________________                                    

In addition to these, thixotropy promoting agent, water-retentive agent,antiseptic agent, rust inhibitor, defoaming or surface active agent andthe like are conveniently added thereto.

An actual preparation of this paint re-adherence preventing component isthe same as that for preparing the paint peeling component.

Experiments were carried out using the above paint peeling composition.

EXAMPLE 1

The duckboard coated with the paint peeling composition and anotherpiece of duckboard un-coated with the paint peeling composition wereleft intact at a painting site for 6 days until unnecessary paint havingthickness of 6.2 mm on the average was accumulatedly adhered to both ofthe boards. The employed paint is a thermosetting baking paint.

Firstly, caustic soda liquid (concentration: 200 g/l, boilingtemperature 105° C.) as a paint peeling bath was prepared and then thebuck boards were dipped in this bath to measure paint peeling time.

In the case of the duckboard coated with the paint peeling composition,the unnecessary paint was completely peeled off the board in 90 secondswithout leaving any trace thereof. On the other hand, in the case of theduckboard un-coated with the composition, even after the board wasboiled in the bath for 8 hours, only about 50% of the bare surface ofthe board was exposed with the other 50% thereof still covered with theunnecessary paint of approximately 0.1 mm in thickness.

After the above paint peeling operations, the peeled-off paint wasfloating as minute particles in the bath as a whole. Thus, a filter wasnecessary to collect the same.

Though as a rough time measurement, the paint peeling time was shortenedto 1/320 with the use of the paint peeling composition. That is to say,the fuel cost and the labor cost for continuously boiling the bath weresignificantly reduced.

However, the caustic soda liquid is not desirable as the paint peelingbath because of the troublesome waste liquid processing and waste paintcollecting and also of the human health hazard and the like. Therefore,the same experiment was carried out, this time, using the paintre-adherence preventing composition related to the present invention asthe paint peeling bath. More particularly, the paint re-adherencepreventing composition diluted by 20 times as much water was used as thepaint peeling bath.

As the result, in the case of the duckboard precoated with the paintpeeling composition, the unnecessary paint was completely peeled off in90 seconds. On the other hand, in the case of the duckboard un-coatedwith the paint peeling composition, only the surface there lost itsvisosity. Since this paint peeling bath has no paint resolvingcharacteristics, the experiment was stopped after 90 seconds.

After the above experiment, the paint peeling bath remained transparentwith the peeled-off paint floating in a non-viscous condition on thesurface of the liquid in the form of ball and the like. Thus, the paintwas easily collected by a simply constructed mesh. Further, when thepaint peeling bath was cooled, the then-floating paint sank as a mass tothe bottom of the tank, and thus, was easily collected at one time. Thecollected mass was non-viscous.

As described above, with the use of the paint peeling bath containingthe paint re-adherence preventing composition, because of the effect ofthe paint re-adherence preventing composition, it is possible to easilycollect the peeled-off paint as a mass without the paint sticking toother objects. And at the same time, the paint peeling bath may bereusable for a long period of time only by adding thereto an amount ofwater equal to that evaporated in the heating. In this way, the workingefficiency is considerably improved and maintanance cost is considerablyreduced since there is no need for waste liquid processing. Moreover,the working environment is also considerably improved since this paintpeeling bath poses no human health hazard.

EXAMPLE 2

The paint peeling composition of the present invention was sprayed overthe floor of the working site to form a coating thereon of approximately0.4 mm in thickness. After air-drying for 6 hours, the dried coating hada thickness of 0.1 mm. Then, the coated floor was left intact for 1 houruntil unnecessary paint was accumulatedly adhered thereon of 7.3 mmthickness.

Thereafter, the boiling paint peeling composition used in Example 1 wasgradually spilled on the floor from its end with lifting up a peeled-offportion and spilling the composition between the floor face and thepaint film, the paint was completely peeled off at a rate of 1 m perabout 7 minutes. Also, because of the effect of the paint re-adherencepreventing composition of the present invention, the paint lostviscosity and was peeled off as a sheet.

EXAMPLE 3

Experiments were conducted for peeling off excess paint by using a paintpeeling composition containing acrylic resin emulsion as its base resin.

The paint peeling composition consisted of:

    ______________________________________                                        acrylic emulsion solids (i.e.,                                                                       10     wt. %                                           acrylic resin)                                                                synthetic resin micro balloons                                                                       9      wt. %                                           thixotropy promoting agent                                                                           3      wt. %                                           water-retentive agent  1      wt. %                                           surface active agent   0.5    wt %                                            water                  75.5   wt %                                            ______________________________________                                         Note: The acrylic resin is emulsified in water and the acrylic emulsion       solids specified above is the weight proportion of acrylic resin on a         solids basis based on the weight of the entire paint peeling composition.

The above-specified paint peeling composition was applied to a gratingto form a film of the paint peeling composition thereon.

The thus prepared grating was left in an actually operating paintingbooth for one week, whereby excess paint was accumulated thereon 5 mm inthickness.

Then, the above grating with the excess paint was submerged in a 95° C.paint-peeling solution bath containing caustic sode at 10 g/lconcentration. The excess paint was completely removed off the gratingwithin 3 minutes.

Since the concentration of the above paint-peeling bath employed in theexperiment was as low as only 1/20 of that (200 g/l) normally employed,the post treatment was very easy. In this respect also, the usefulnessof the composition of the present invention will be fully appreciated.

Further, substantially the same results were achieved also when a vinylacetate emulsion was employed in place of the acrylic emulsion to resultin the same weight percentage proportion of resin.

EXAMPLE 4

Experiments were conducted for obtaining a critical range of the acrylicemulsion solids content in the paint-peeling composition. In theseexperiments, the contents of the composition were the same as those inthe above Example 3 and only the weight ratio between the acrylicemulsion solids content and the water content was varied as theparameter.

(1) Experiments for Obtaining Lower Limit Value (A) Composition ofPaint-Peeling Composition

    ______________________________________                                                        experiment 1                                                                           experiment 2                                         ______________________________________                                        acrylic emulsion solids content                                                                 1 wt. %    2 wt. %                                          ______________________________________                                    

(B) Method and Results of Experiment

(a) Operability

With the composition of experiment 1, there occurred precipitation ofsynthetic resin balloons in the course of operation, which actuallydisabled the operation. Then, in order to prevent this precipitation,the amount of thixotropy promoting agent was increased. However, thisonly resulted in prolongation of drying time and brittleness of thecoating per se.

With the composition of experiment 2, there occurred no such problem.

(b) Applicability

Since the composition of experiment 1 is low in viscosity, the coatingtended to be thin at edge portions of the grating and also was repelledfrom portions of the surfaces to be coated contaminated with oilysubstances.

The composition of experiment 2 had no such problems in these respectsalso.

(c) Strength of Coating

As described hereinbefore, with the composition of experiment 1, thecoating formed tends to be thin. Therefore, the coating was easilyremoved by stepping of safety boots.

On the other hand, the composition of experiment 2 sufficientlywithstood the safety boots stepping test.

(C) With the above observations, it was concluded that the acrylicemulsion solids content should be a minimum of 2 wt. %.

(2) Experiments for Obtaining Upper Limit Value (A) Composition ofPaint-Peeling Composition

    ______________________________________                                                        experiment 3                                                                           experiment 4                                         ______________________________________                                        acrylic emulsion solids content                                                                 12 wt. %   14 wt. %                                         ______________________________________                                    

(a) Operability

With the composition of experiment 4, there occurred four problemslisted below:

1. In the winter season, the viscosity increased up to someten-thousands of cps and the composition became unusable.

2. Removal of excess composition from the applying brush was verytime-consuming and inefficient.

3. Since the formed coating was considerably thick, it took a long timeto dry on intricate surfaces such as the interior of grating.

4. When a plurality of gratings were placed one on another, thecomposition, when dried, acted as an adhesive. Thus, it was troublesometo separate the gratings again.

On the other hand, the composition of experiment 4 was free from suchproblems since its viscosity and coating thickness were appropriate.

(b) Costs

With the composition of experiment 4, because of its high viscosity, thegrating tended to be coated with excessive amount of composition. Forthe same reason, there also occurred costly waste of compositionremaining on the container and the brush.

The composition of experiment 3 presented no such problems at all.

(C) From the above experiment results, it was concluded that the acrylicemulsion solids content should be no higher than 12 wt %.

(3) Critical Values

From the above experiments, it was concluded that the acrylic emulsionsolids content should be no less than 2 wt. % and no greater than 12 wt.%.

Essentially the same results were obtained when polyvinylacetateemulsion was employed in place of the acrylic emulsion.

What we claim is:
 1. An aqueous paint peeling composition for forming acoating on a surface of an object thereby to permit ready removal ofundesired paint subsequently applied onto the coating surface,comprising as effective components thereof:2 to 12 weight percent of anacrylic resin or polyvinylacetate; and a substance which when heated isin the form of minute shells enclosing a gas or vapor, the shells beingthermally expandable without rupturing.
 2. A composition as claimed inclaim 1, wherein said substance is at least one of shirasu balloons,glass balloons, carbon balloons, foamed synthetic resin balloons andunfoamed synthetic resin which is heat foamable to form synthetic resinballons.
 3. A composition as claimed in claim 1, wherein said substanceis thermally expandable at a temperature higher than a dryingtemperature of the excess paint.
 4. A composition as claimed in claim 1,wherein said substance is foamed synthetic resin balloons.
 5. Acomposition as claimed in claim 1, wherein said substance is unfoamedsynthetic resin which is heat foamable to form synthetic resin balloons.